This week, we're meeting ruthenium, a chemical element that even I'd forgotten about! Ruthenium has the symbol Ru and the atomic number 44. This rare element was named for the area of Eastern Europe that includes present-day western Russia, Ukraine and Belarus, as well as parts of Poland and Slovakia. As you can see in the above image, ruthenium is a hard, lustrous silvery metal. It is in the precious metal, or platinum, group (group 8) of the periodic table.

One of the rarest metals on earth, ruthenium is becoming increasingly valuable as we better understand just how useful it is. Ruthenium does not tarnish at room temperatures, nor is it attacked by hot or cold acids or by aqua regia (which can dissolve gold). Resistance to corrosion is one of ruthenium's important qualities: adding tiny amounts of ruthenium to create alloys with other metals likewise makes them corrosion-resistant and also strengthens them. These alloys are commonly used in platinum jewelry and in electrical contacts that must resist wear. Currently, 50 percent of the ruthenium is used by the electronics industry and 40 percent is used by the chemical industry, whilst the remainder is primarily used to create alloys of platinum (for jewelry) and titanium (for corrosion-resistant underwater pipes).

Ruthenium has no known biological role nor is it poisonous, although ingested ruthenium is concentrated and retained by the bones.

Many of us have met ruthenium whilst admiring expensive writing instruments. Parker pens uses ruthenium to make the nib of its "RU" fountain pen: the nib is 14-carat gold with a ruthenium tip.

Here's the Professor telling us a little more about ruthenium, and he's also correcting an "embarrassing" mistake in the first version of this video: